Note: Descriptions are shown in the official language in which they were submitted.
CA 02874602 2014-12-12
Attorney Docket No: 2013P16966US
ABRASIVE CLEANING OF INNER COOLED GENERATOR COILS
FIELD OF INVENTION
[0001] The application relates to abrasive cleaning of inner cooled generator
coils.
BACKGROUND OF INVENTION
[0002] A precise surface management is always a challenge for inner cooled
generator coils. An
inner cooled generator coils have a plurality of hollow conductors, a
plurality of solid conductors
and an insulation system. Cooling passages of the inner cooled generator coils
are formed by the
hollow conductors.
[0003] During operation of the generator, deposits or products of corrosion
accumulate on inner
walls of the hollow conductors. The accumulated deposits or products of
corrosion increase the
dynamic flow losses of the fluid cooling medium and impedes heat conduction
from the hollow
conductors to the fluid cooling medium. The decrease of heat removal through
the fluid cooling
medium requires maintenance to the generator coils to remove accumulated
deposits or products
of corrosion from the inner walls of the hollow conductors.
[0004] Due to small cross section of each hollow conductor in the inner cooled
generator coils,
the accumulated deposits or products of corrosion are hard to remove. A
diameter of the cross
section of each hollow conductor in the inner cooled generator coils is in a
range of 0.5 mm to 2
mm.
[0005] Mechanical method, such as machining the base metal of the hollow
conductors to remove
the deposits or products of corrosion, is not suitable for the inner cooled
generator coils because
of the small cross sections of the hollow conductors. The machining method
also damages the
base metal of the hollow conductors. The shape of the coils in generators
incorporates an involute
curve on the end which also makes a mechanical removal by machine tools not
possible.
[0006] Chemical cleaning method uses acids to remove deposits or products of
corrosion. This
method often damages the base metal of the hollow conductors and incomplete
removal can result
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in failure of pressure boundary of the hollow conductors as the chemical
action continues after
flushing the acids.
SUMMARY OF INVENTION
[0007] An efficient and precise surface management that may remove deposits or
products of
corrosion of an inner cooled generator coils without damaging the base metal
of the hollow
conductors is provided.
[0008] This objective is achieved by the features of the independent claim.
The dependent claims
define embodiments.
[0009] The objective is achieved by applying a shear hardening fluid medium
with suspended
abrasive particles which removes deposits or products of corrosion and polish
the insides of
, cooling passages down the micron level. Small convoluted passages may be
cleaned using the
proposed method.
[0010] According to an embodiment, an inner cooled generator coil includes a
plurality of hollow
conductors. Cooling passages of the inner cooled generator coil are formed by
the hollow
conductors. Each of the hollow conductors has a small cross section. For
example, a diameter of
the cross section of the hollow conductor is between 0.5 mm to 2 mm in an
industrial practice.
[0011] During the operation of the generator, deposits or products of
corrosion accumulate on
inner walls of the hollow conductors. The accumulated deposits or products of
corrosion
increases the dynamic flow losses of the fluid cooling medium and impedes heat
conduction from
the hollow conductors to the fluid cooling medium. The decrease of heat
removal through the
fluid cooling medium requires maintenance to the generator coil to remove the
deposits or
products of corrosion from the inner walls of the hollow conductors.
[0012] According to an embodiment, a shear hardening medium is filled into the
cooling passage
of the generator coil. Abrasive particles are suspended in the shear hardening
medium.
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[0013] According to an embodiment, a hydraulic pressure is applied to the
shear hardening
medium. The hydraulic pressure locks the suspended abrasive particles into a
matrix position. A
matrix position is a semiregular arrangement of the particles in the shear
hardening medium that
provides the abrasive action at the interface to the cooling passage. The
shearing hardening of the
shear hardening medium is a function of the applied hydraulic pressure. The
applied hydraulic
pressure locks the abrasive particles into the matrix position and does not
exceed a capability of
the hollow conductors to hold the pressure. The applied hydraulic pressure,
for example, may be
in a range of 100 psi to 1,000 psi, or in a range of 200 psi to 800 psi , or
in a range of 300 psi to
600 psi.
[0014] According to an embodiment, a flow is imparted to the shear hardening
medium within
the cooling passage. The flow applies a shear hardening force to the shear
hardening medium. The
deposits and products of corrosion are removed from inner wall of the cooling
passage by the
. shear hardening force and the abrasive particles locked in the shear
hardening medium.
[0015] According to an embodiment, after completion of removing the deposits
and products of
corrosion, the hydraulic pressure is released from the shear hardening medium.
[0016] According to an embodiment, the shear hardening medium is flushed out
of the cooling
passage after releasing the hydraulic pressure from the shear hardening
medium.
[0017] According to an embodiment, a shearing hardening medium may be a visco-
elastic
abrasive medium. The medium behaves predominantly as an elastic solid at an
applied strain of
the orbital working motion and applies orbital or other relative working
motion to produce strain
rates which bring the medium into a predominantly elastic deformation.
[0018] According to an embodiment, the visco-elastic abrasive medium may be a
rheopectic poly
filled with viscosity increasing stiffening agents and loadings of abrasive
particles.
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[0019] According to an embodiment, the shearing hardening medium may be a
semisolid polymer
composition.
[0020] According to an embodiment, the abrasive particles may be commonly used
industrial
abrasive particles, such as aluminum oxide, or silicon carbide, or sand, or
diamond, or steel
abrasives, etc., or combinations thereof.
[00211 According to an embodiment, the shear hardening medium entirely fills
the cooling
passage of the generator coil so that the entire cooling passage is cleaned
during the cleaning.
[0022] According to an embodiment, the flow may be imparted within the cooling
passage as a
single pass cleaning having a unidirectional flow.
[0023] According to an embodiment, one header used for the cleaning is
attached to one end of
- the generator coil and connected to a hydraulic pump by a high pressure
flexible hose in the single
pass cleaning.
[0024] According to an embodiment, the flow may be imparted within the cooling
passage as a
reciprocated pass cleaning having alternative flow.
[0025] According to an embodiment, one head used for the cleaning is attached
to each end of the
generator coil and connected to a hydraulic pump by a high pressure flexible
hose respectively in
the reciprocated pass cleaning. The header will be removed after the cleaning
A frequency of the
alternative flow, for example, may be in a range of 1,000 Hz to 10,000 Hz, or
in a range of 1,200
Hz to 8,000 Hz, or in a range of 1,400 Hz to 6,000 Hz.
[0026] According to an embodiment, the shear hardening medium is passed in the
cooling
passage at a high speed so that the shearing hardening force is increased and
the abrasive particles
are firmly locked in the position. The passing speed, for example, may be in a
range of 1 m/s to
m/s, or in a range of 2 m/s to 9 m/s, or in a range of 3 m/s to 7 m/s.
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[0027] According to an embodiment, the generator coil is cooled by cooling
medium, such as by
cooling water, or by cooling air, or by hydrogen, etc.
[0028] Various aspects and embodiments of the application as described above
and hereinafter
may not only be used in the combinations explicitly described, but also in
other combinations.
Modifications will occur to the skilled person upon reading and understanding
of the description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Embodiments of the application are explained in further detail with
respect to the
accompanying drawings. In the drawings:
FIG 1 shows a cross section of an inner cooled generator coil;
FIG 2 shows an apparatus for performing a single pass cleaning;
FIG 3 shows an apparatus for performing a reciprocated pass cleaning;
FIG 4 shows a longitudinal cross section of a hollow conductor with fluid
cooling medium;
FIG 5 shows a longitudinal cross section of a hollow conductor with
deposits;
FIG 6 shows a longitudinal cross section of a hollow conductor with a shear
hardening fluid
medium;
FIG 7 shows the shear hardening fluid medium with shear hardening force
inside the hollow
conductor;
FIG 8 shows a single pass cleaning with broken off deposits;
FIG 9 shows a reciprocated pass cleaning with broken off deposits;
FIG 10 shows flow of flushing medium to flush out the shear hardening fluid
medium from
the hollow conductor.
DETAILED DESCRIPTION OF INVENTION
[0030] While specific embodiments have been described in detail, those with
ordinary skill in the
art will appreciate that various modifications and alternative to those
details could be developed
in light of the overall teachings of the disclosure. For example, elements
described in association
with different embodiments may be combined. Accordingly, the particular
arrangements disclosed
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are meant to be illustrative only and should not be construed as limiting the
scope of the claims or
disclosure, which are to be given the full breadth of the appended claims, and
any and all
equivalents thereof. It should be noted that the term "comprising" does not
exclude other elements
or steps and the use of articles "a" or "an" does not exclude a plurality.
[0031] FIG 1 shows a cross section of an inner cooled generator coil 1. The
inner cooled
generator coil 1 includes a plurality of hollow conductors 2, a plurality of
solid conductors 3 and
an insulation system 4. Cooling passages of the inner cooled generator coil
are formed by the
hollow conductors 2. Each of the hollow conductors 2 has a small cross
section. A diameter of the
cross section of the hollow conductors 2, for example, is between 0.5 mm to 2
mm.
[0032] FIG 2 shows an apparatus for performing a single pass cleaning. One
header 5 is attached
to one end of the generator coil 1. FIG 3 shows an apparatus for performing a
reciprocated pass
cleaning. One header 5 is attached to each end of the generator coil 1
respectively. The header 5 is
connected to the hydraulic pump 7 by a high pressure flexible hose 6.
[0033] During operation of the generator, the generator coil 1 is cooled by
fluid cooling medium
8 within a cooling passage 9. The cooling passage 9 is formed by the hollow
conductor 2 having
an inner wall 10, as shown in FIG 4. The fluid cooling medium 8 may be cooling
water, or
cooling air, or hydrogen, etc.
[0034] During the operation of the generator, deposits or products of
corrosion 11 accumulate on
the inner wall of the hollow conductors 2, which are shown in FIG 5. The
accumulated deposits
or products of corrosion 11 increases the dynamic flow losses of the fluid
cooling medium 8 and
impedes heat conduction from the hollow conductors 2 to the fluid cooling
medium 8. The
decrease of heat removal through the fluid cooling medium 8 requires
maintenance to the
generator coil 1 to remove the deposits or products of corrosion 11 from the
inner walls of the
hollow conductors 2.
[0035] According to an embodiment, the cooling passage of the hollow conductor
2 is filled with
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a shear hardening medium 12 during the maintenance, which is shown in FIG 6.
The shear
hardening medium 12 has abrasive particles suspended therein. The shear
hardening medium 12
may be, for example, a visco-elastic abrasive medium, or for example, a
rheopectic poly filled
with viscosity increasing stiffening agents and loadings of the abrasive
particles, or for example, a
semisolid polymer composition.
[0036] According to an embodiment, the shear hardening medium 12 is applied
with a hydraulic
pressure. The hydraulic pressure locks the abrasive particles suspended in the
shear hardening
medium 12 into a matrix position. A matrix position is a semiregular
arrangement of the particles
in the shear hardening medium that provides the abrasive action at the
interface to the cooling
passage. The viscosity of the shear hardening medium is partly a function of
the hydraulic
pressure. The applied hydraulic pressure locks the abrasive particles into the
matrix position and
does not exceed a capability of the hollow conductors to hold the pressure.
The applied hydraulic
pressure, for example, may be in a range of 100 psi to 1,000 psi, or in a
range of 200 psi to 800
, psi, or in a range of 300 psi to 600 psi.
[0037] According to an embodiment, a flow is imparted to the shear hardening
medium 10 within
the cooling passage in the hollow conductor 2. A shearing hardening force 13
is applied to the
shear hardening medium 12 by the imparted flow, as shown in FIG 7.
[0038] FIG 8 shows an embodiment of a single pass cleaning. In the single pass
cleaning, a
unidirectional flow 14 is applied to the shear hardening medium 12 so that
shear hardening
medium 12 moves inside the hollow conductor 2 in one direction while under
pressure. The flow
of the pressurized shear hardening medium 12 and the locked abrasive particles
15 abrade the
deposits or products of corrosion 11 into broken off deposits or products of
corrosion 16.
[0039] FIG 9 shows an embodiment of a reciprocated pass cleaning. In the
reciprocated pass
cleaning, alternative flows 17 are applied to the shear hardening medium 10 so
that the shear
hardening medium 12 moves inside the hollow conductor 2 in alternative flow
directions while
under pressure. The alternative flow of the pressurized shear hardening medium
10 and the
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locked abrasive particles 13 abrade the deposits or products of corrosion 11
into broken off
deposits or products of corrosion 16.
[0040] According to an embodiment, the shear hardening medium 12 moves inside
the hollow
conductor 2 for a sufficient period of time so that the deposits are abraded
from the inner walls of
the hollow conductor 2. At the completion of the abrasion, the shear hardening
medium 12 is
released from the hydraulic pressure and drained from the hollow conductors 2.
FIG 10 shows the
residue of the shear hardening medium 12 is flushed out of the hollow
conductor 2 by a flushing
medium 18.
[0041] After flushing out the shear hardening medium 12 from the hollow
conductor 2, the
generator coil 1 is returned to service with unimpeded flow of the cooling
medium item 8 to
provide adequate heat removal.
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List of references:
1 generator coil
2 hollow conductor
3 solid conductor
4 insulation system
5. header
6 flexible hose
7 hydraulic pump
8 fluid cooling medium
9 cooling passage
inner wall of the hollow conductor
11 deposits or products of corrosion
12 shearing hardening medium
13 shear hardening force
14 unidirectional flow of the shearing hardening medium
abrasive particles
16 broken off deposits or products of corrosion
17 alternative flows of the shearing hardening medium
18 flushing medium
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